1. Field of the Invention
The present invention relates to an image display apparatus using an electron source.
2. Related Background Art
Japanese Patent Application Laid-Open H03-261024 discloses a spontaneous light emitting type flat display, which displays an image by illuminating a phosphor with an electron beam emanated from an electron source to generate fluorescence. The flat display is a thin image display apparatus constituted by placing an electron-emitting device for generating an electron beam within a vacuum panel sandwiched between a face plate and a rear plate. In the image display apparatus, a surface conduction electron-emitting device is employed as the electron-emitting device, and the electron beam is accelerated and irradiated onto the phosphor to cause the phosphor to emit light for displaying an image.
Japanese Patent Application Laid-Open H11-250839 discloses an image display apparatus with reduced halation, which is caused by back scattering electrons, generated by a phosphor illuminated with an electron beam, reentering the phosphor and causing it to emit light in unwanted portions; providing high-definition, high-contrast and purer spectral colors.
FIG. 4 is a schematic sectional view illustrating a planar image display apparatus disclosed in Japanese Patent Application Laid-Open H11-250839.
In this image display apparatus, an electron-emitting device 202 is formed on an insulating substrate 201. A grid 204 is a modulating electrode having a passage hole for the electron beam, and is mounted on an insulating layer 203. A transparent conductive ITO (indium tin oxide) film 211, a phosphor 206 and an aluminum film 210 provided for improving luminous efficiency are formed on the panel side of a face plate substrate 205, over which a graphite film 207 is formed to avoid back scattering electrons.
An electroconductive capturer 213 has an opened portion 214 for passing an electron ray emanated from the surface conduction electron-emitting device 202, and an unopened portion 215 for capturing the back scattering electrons from the face plate substrate 205 side, and is maintained at a predetermined distance from the face plate by means of a partition member 216.
Using glass frit 208, the face plate substrate 205 and the substrate 201 are sealed, having an outer frame 209 in-between, to constitute a vacuum enclosure. A surface conduction electron-emitting device 202 is connected to an outer drive circuit (not shown), and the graphite film 207, aluminum film 210 and ITO film 211 are connected to a high voltage power supply (not shown) by a high voltage cable which is not shown.
In the image display apparatus described above, the internal pressure is maintained at vacuum of approximate 10−4 Pa, and electrons are emanated in the form of an electron beam when driving pulse voltage is applied to the surface conduction electron-emitting device 202 by the outer drive circuit. The electron beam passes the grid 204, and is accelerated by positive high voltage applied to the phosphor 206 and the aluminum film 210 from the high voltage power supply to emit fluorescence upon impinging on the phosphor 206.
As an electron source, in addition to using a surface conduction electron-emitting device, it is known to use a thermal electron source using a hot cathode, a field emission type electron-emitting device or a metal/insulating layer/metal type electron-emitting device.
In a planar image display apparatus as described above, the smaller opened portion of the electroconductive capturer increases the capture rate of the back scattering electrons, and as a result, improves the effect of reducing halation. However, the opened portion also functions to pass an electron beam (primary electron) emanated from the electron source, and the smaller opened portion prevents more primary electrons from passing through, reducing brightness and luminous efficiency. For this reason, a problem arises in that it has been difficult to make the opened portion smaller to a width such that enough back scattering electrons can be captured, which results in poor reduction of halation.